1. Field of the Invention
The present invention primarily relates to a response membrane for use in a chloride ion selective electrode for measuring a sample containing blood or protein. It is an object of the present invention to provide a response membrane capable of containing a stable reading or measurement of (Cl.sup.-) without drifting during the measurement and without being subjected to interferences by other ions. Further, by use of the response membrane of the present invention, it is possible to measure chlorine ions with a high degree of accuracy and the response membrane is superior in linearity to other known membranes.
2. Description of the Prior Art
There have been known the following three types of methods for producing a response membrane for use in a chloride ion selective electrode:
(a) A method for forming a response membrane made of a solid molded membrane chiefly comprising silver chloride;
(b) A method for producing a response membrane by enclosing a responsive substance and a solvent in a plastic membrane made of vinyl chloride; and
(c) A method for producing a response membrane by holding a responsive subject dissolved in a suitable organic solvent in a porous membrane.
However, when a response membrane produced according to the method (a) is used, both the phenomenon of drift and hunching are increased if the measurement is carried out on blood without diluting it, thereby giving rise to inaccurate measurements. At this time, if the response membrane is once influenced by the interference of a protein, the indication or reading does not return to the original reading, even if the interfering ions are eliminated. In addition, a response membrane of this type has such a disadvantage that the influence by a protein and the like cannot be removed even though the surface of the response membrane is coated with a hydrophobic polymer, such as DURAGUARD and the DURAGUARD coat must be exchanged once every two weeks.
When a response membrane produced according to the method (b) is used, the chloride ion selective electrode has such a disadvantage that it is inferior in linearity, the drift in the serum is increased, and the span of life of the electrode is remarkably shortened to about two weeks.
A liquid membrane type electrode produced according to method (c) has such disadvantages in that the span of life is shortened since the sample is contaminated with the organic layer, and the electrode is complicated in construction, even though the porous membrane is made to be exchangeable, and it requires maintenance, which is time consuming. This type of electrode also has such disadvantages that it is inferior in mechanical strength, and is particularly weak against vibration.